EVOLUTION

• Biological evolution


  Descent with modification
• Microevolution


  Small-scale genetic change within a species
• Macroevolution


  Large-scale evolutionary events such as the emergence of new species
• Evolutionary thought has evolved for centuries
• Explanations proposed for life's diversity

  • Belief in a creator
  • Geology laid the groundwork for evolutionary thought
  • Lower rock layers are older than those above, suggesting an evolutionary sequence for fossils within them
  • Lamarck proposed a testable mechanism of evolution, but it was erroneously based on use and disused of traits acquired during an organism's life
• Charles Darwin's voyage


  • Observed the distribution of organisms in diverse habitats and their relationships to geological formations
  • Developed his theory of the origin of species by means of natural selection
• Natural selection


  • Based on multiple observations: individuals vary for inherited traits; many more offspring are born than survive; and life is a struggle to acquire limited resources
  • The environment eliminates poorly adapted individuals, so only those with the adaptations reproduce
  • Artificial selection is based on similar requirements, except that a human breeder decides exactly which individuals reproduce
• On the Origin of Species offered abundant evidence for descent with modification
• The modern evolutionary synthesis unifies ideas about DNA, mutations, inheritance, and natural selection
• Adaptation


  Species modify their phenotypes in ways that permit them to succeed in their environment
• Speciation


  The number of species multiplies; a single species can give rise to two or more descendant species
• Darwin maintained that all species are related; any two species on earth today have shared a common ancestor at some point in their history
• Clues to evolution


  • The geologic timescale
  • Paleontology (the study of past life)
  • Biogeography
  • Comparisons of the physical and biochemical characteristics of species
• Fossils


  Remains of ancient organisms
• The fossil record is often incomplete as many organisms that lived in the past did not leave fossil evidence
• Relative dating


  The position of a fossil in the context of others provides a relative date
• Radiometric dating


  Uses radioactive isotopes to estimate the absolute date when an organism lived
• Biogeography


  The study of the distribution of species on Earth
• Plate tectonics theory


  Forces deep inside Earth have moved the continents throughout much of life's history, creating and eliminating geographical barriers
• Biogeography provides insights into large- and small-scale evolutionary events
• Homologous structures


  Have a shared evolutionary origin, although they may differ in function
• Vestigial structures


  Have no function in an organism but are homologous to functioning structures in related species
• Analogous structures


  Similar in function but don't reflect shared ancestry
• Convergent evolution can produce analogous structures
• Differences between homologous and analogous structures


  • Homologous: Similar structure, differing function, from a common ancestor
  • Analogous: Similar function, similar structure, not from a common ancestor
• Evolutionary developmental biology


  Combines the study of development with the study of DNA sequences
• Homeotic genes


  Influence the development of an organisms' body parts; mutations in homeotic genes may lead to new phenotypes
• Molecular clock


  Compares DNA sequences to estimate the time when two species diverged from a common ancestor
• Natural selection


  Molds evolution by eliminating poorly adapted phenotypes and allowing individuals with the best adaptations to the current environment to leave more offspring
• Natural selection requires variation, which arises ultimately from random mutations
• Natural selection does not have a goal and cannot achieve perfectly adapted organisms
• Evolutionary fitness


  Organisms with the highest evolutionary fitness are the ones that have the greatest reproductive success
• Ways natural selection can shape populations


  • Directional selection: one extreme phenotype becomes more prevalent
  • Disruptive selection: two or more extreme phenotypes survive at the expense of intermediate forms
  • Stabilizing selection: an intermediate phenotype has an advantage over individuals with extreme phenotypes
• Harmful recessive alleles may persist in populations where heterozygous carries have a reproductive advantage over homozygotes
• Hardy-Weinberg equilibrium


  Allele frequencies do not change from generation to generation
• The conditions for Hardy-Weinberg equilibrium do not occur together in natural populations, suggesting that allele frequencies always change from one generation to the next
• Mechanisms of evolution


  • Natural selection
  • Mutation
  • Genetic drift
  • Nonrandom mating
  • Migration
• Natural selection


  The process by which individuals with beneficial traits are more likely to survive and reproduce, leading to the evolution of new species over time. This is the currently accepted explanation for the evolution of life on Earth.
• Lamarckism


  The idea that an organism can acquire traits during its lifetime and pass those traits on to its offspring. This theory has been discredited by modern science.